It is known that, when a sound wave emitted in a closed room encounters a surface, part of its energy passes through the surface, part is absorbed by the impact with the surface and part is reflected into the room.
If, in a room, the reflective surface area is high, the room may be acoustically very disturbed since the sound waves produced inside it are amplified with an effect similar to that of an echo.
In order to improve the acoustics of a room, without structural modifications, it is known to provide in the room one or more sound-absorbing panels for absorbing a large part of the energy.
The acoustic correction measures involve lining the internal surfaces of the rooms with sound-proofing materials; they must have not only acoustic but also aesthetic characteristics suitable for allowing them to blend in with the interior design and furnishings.
Sound-proofing materials have the property that they absorb at least a part of the acoustic energy and reduce the amount of reflected energy.
The known sound-proofing panels, to be applied for example to a wall, have a structure composed of a layer of foam (for example foam rubber) lined with a sheet and kept rigid by a perimetral frame made of metal (for example aluminium), plastic or wood. The sheet is typically wound around the perimetral frame so as not to show, at least on a visible side, stitching or other joints. However, when a sound-proofing panel must have two visible sides, it is more difficult to mask a joint in the sheet in a zone where one edge of the sheet overlaps the other edge of the sheet.
In other known panels, the padding layer is combined with a rigid surface (for example made of metal, plastic or wood) which increases the rigidity thereof. The rigid surface may be positioned on one side of the padding or inside the padding itself, creating a sandwich structure.
A first drawback of the sound-proofing panels made according to the prior art consists in the presence of the frame or support surface. They may in fact have a considerable weight and therefore be difficult to handle, install and support; moreover often the frame or the support surface constitute the most costly item of the panel.
Another drawback, as already mentioned, is that the sound-proofing panels must have not only good sound-absorbing properties, but also satisfactory aesthetic characteristics since they must blend in with the interior design and the furnishings. The frame and the joints between two sheet edges used to cover the panel undoubtedly constitute unattractive features which do not blend in with the surroundings.
The problem which arises is that of providing a joining element for connecting together, in substantially hinged fashion, two or more panels in a simple, low-cost and removable manner.